Non-polar olefin resins such as polypropylene, polyethylene, an ethylene-propylene copolymer rubber, and a styrene-butadiene-styrene block copolymer are inexpensive and have excellent resistance to organic solvent, and are used in production of car exteriors such as a bumper and a side molding. These resins are used alone or in combination with each other as described, for example, in Japanese Pat. Application Nos. 134106/84 and 154570/84.
These resins, however, are poor in weathering properties. To improve such poor weathering properties, paint coating is applied on the surface of moldings, or a ultraviolet absorber and pigments such as titanium oxide and carbon black are compounded to the resin and the resulting mixture is kneaded and molded to obtain a product.
In the case of production of large-sized molded particles having a large thickness, the above latter method is not advantageous in that large amounts of expensive ultraviolet absorbers and pigments are necessary to compound. Therefore the above former method to coat the surface of molded articles is suitable for practical use. However, since the olefin resins are composed of non-polar elements such as hydrogen and carbon, it is difficult to adhere the paint directly to the resins. For this reason, the surface of molded articles is generally subjected to oxidation treatment such as treatment using chemicals, plasma treatment and flame treatment, or a primer composed mainly of chlorinated polypropylene, maleic anhydride-grafted polypropylene, and maleic anhydride-modified chlorinated polypropylene is coated and dried to form an overcoating.
With conventional primers, however, the adhesion between the olefin resins and the coating is not sufficiently high; they have a disadvantage in that the coating is peeled off from the molded articles during use, resulting in reduction of the appearance.